Get Focused! Understanding your Camera’s Autofocus

June 25, 2014

Get Focused! Understanding your Camera’s Autofocus

Ensuring that your images are tack sharp is a fundamental skill in all photography. And an important part of that is learning to use and control your camera's autofocus system.

At first blush, using autofocus would appear to be pretty self-explanatory. It's point and shoot, right? And that would seem to be especially true given the sophistication of today's digital cameras.

But we all know that it's not always that easy. How many times have you snapped a shot that looked razor crisp in the viewfinder just to find that it's just not so when you pull the image up on your computer screen when you get back home? You may find that the whole image is just a bit soft or, worse yet, that a part of the photo is in perfect focus, but it's the wrong part.

UGH!

So to get the most from your camera's autofocus, it's important to understand how to work with the system and how the different settings affect the way your camera focuses on the scene in the viewfinder. It's just those settings that can be a bit confusing. But I think this confusion has a lot to do with terminology. So let's see if we can straighten a few things out.

The first thing that you need to know about your camera's autofocus system is that there are actually TWO settings that control how your camera focuses on the scene in the viewfinder:

  • The first of these settings is called the AF-Area Mode on Nikon and the AF point Selection Mode on Canon. In our discussion here, for simplicity we'll refer to this as the Area Mode.
  • The second setting is called the Focus Mode on Nikon and the AF Shooting Mode on Canon. Here, we'll call this the Focus Mode.

Here's the important thing to remember about this two modes:

The Area Mode controls WHERE your camera focuses.

The Focus Mode controls WHEN and HOW your camera focuses.

Let's look at each of these in a little more detail.

Area Mode

If you look through the viewfinder of your DSLR, you'll see an array of squares or brackets superimposed over the scene visible through the lens. The number and arrangement of these squares vary between brands and even from camera to camera within a brand, but in general they look something like this:

using autofocus

These markings are called focus points and they indicate where your camera will set focus within the scene. So whichever of these points is selected, or "active", determines what area of your image will be in focus.

The camera's Area Mode dictates how that active focus point is chosen.

Most cameras give you a choice of between 3 to 4 Area Modes but they're all variations of these two basic modes:

  • Automatic Point Selection

    This is the default mode on most cameras. In this mode, the camera decides which focus point to use.

    Some cameras set the focus point on the object closest to the camera and some cameras use a more complex algorithm to identify which focus points coincides with the subject of your image.

    Either way, though, when you're shooting with Automatic Point Selection, the choice of the focus point is up to the camera.

  • Manual Point Selection

    With Manual Point Selection, you choose the active focus point and, so, are able to control exactly what your camera is focusing on.

    With Manual Point Selection, you choose the focus point that you want active by moving a dial pad or a button or a wheel on the back or top of your camera. As you do that, you will see each of the focus points light up one-by-one indicating that it is active. Then, when you press the shutter button, the camera will focus at the place in the scene that coincides with the active focus point.

The important thing to remember about the Area Mode is that, by default, your camera is in charge of deciding the place in the scene that will be sharp and in focus.

Focus Mode

Most cameras offer a choice of 4 to 5 focusing modes. As with the Area Modes, the labels for the different modes vary by brand, but here are the basics:

  • Single Servo/AF-S/One Shot

    In this mode, the camera locks focus when you press the shutter button halfway down and focus stays locks in that position until either the picture is taken or the shutter button. With this mode, focus stays locked regardless of any movement of your camera or your subject.

  • Continuous/AF-C/AI Servo

    In the Continuous focus mode, the camera will continuously focus as long as the shutter button is pressed halfway. So if your subject moves, the camera will reacquire focus to keep that subject sharp and it will keep doing that—updating focus as your subject moves—as long as the shutter button remains half pressed.

  • Auto/AF-A/AI Focus

    In Auto focus, the camera decides for itself which focus mode—Single or Continuous—works best for the scene and switches between the modes as necessary to keep the subject in focus. So if the camera detects subject movement, it switches to Continuous mode. But if there is no movement, it uses Single focus mode.

So that's it. These are the settings and modes that make your camera's autofocus tick.

For more information on all this, check out the two videos below. They are both by the always helpful by Mark Wallace of AdoramaTV .

Enjoy!




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